The economics of castles

When I'm in Britain or Ireland, one of my favourite sightseeing trips is to visit medieval castles. Even the ruined ones are fun to visit. Actually, maybe the ruined ones are more fun to visit, because you get to imagine what they would have looked like in their heyday. Britain and Ireland are full of castles, many of which were built by and housed local nobles. In fact, in relative terms there were very few royal castles, which the literature in history and economic history has interpreted as a sign that centralised states were weak.

However, this recent article by Desiree Desierto and Mark Koyama (both George Mason University), published in the journal European Economic Review (ungated earlier version here) challenges that view. They instead show that there was an economic logic to the proliferation of private castles.

Desierto and Koyama develop a game theoretic model of medieval states, which first recognises that the monarch cannot rule alone but must rely on a coalition of local lords or barons. Each lord agrees to join the coalition, and pledges resources to the monarch in exchange for a (however small) share of control of the kingdom. The monarch can renege on the agreement, taking the resources without offering a share to the lord. However, the lord would then rebel, leaving the coalition. What allows the lord to leave the coalition, and gives them bargaining power, is the presence of their own castles, since they can retreat to their castle when they rebel against the monarch. Without a private castle, the lord would have little bargaining power, and would anticipate the monarch reneging on any agreement, and so they would not join the coalition in the first place. In economic terms, the castle gives the lord an outside option. 

So, the monarch tolerates private castles held by the lords, because the presence of those castles gives the lords the feeling of security they need to join the kingdom. And, in turn, the presence of those castles disciplines the monarch. Rebellions are more costly to suppress when the lords can retreat to a well-defended private castle. The lords' outside option increases the feasibility of rebellion and ensures that the monarch mostly keeps to their agreement with the lords.

In short, the private castles induce an equilibrium where the kingdom is larger and more stable than it would be without them. Notice that this is the opposite of the conventional view that private castles represent a sign that a state was weak.

Desierto and Koyama support their argument with descriptive evidence, noting that:

In Norman England after the Conquest, castles were built across the country: by 1154 there were 225 baronial castles (compared to 49 royal castles) in England... Baronial castles allowed the Dukes of Normandy to extend their authority over the far larger territory of Anglo-Saxon England. Similarly, in the twelfth century Angevin rule expanded over much of France as semi-independent lords in Gascony accepted the lordship of Henry II.

Desierto and Koyama also note that powerful medieval monarchs did not act to systematically eliminate private castles, and in fact the monarchs often gave away their own castles to local lords. And the power of the lords did keep the monarchs in check - a lord's probability of rebelling against the monarch was positively correlated with the number of private castles in the lord's family network. That last point might sound contradictory, but since castles make rebellion by lords a more credible threat, this can deter monarchs from reneging and reduce the number of rebellions overall. However, when rebellion does occur, lords connected to more castles were more likely to participate in the rebellion.

So, if private castles were so important for the stability of medieval states, why did private castles eventually disappear? Desierto and Koyama note that:

The answer is military technology, not the rising power of the state. Technological changes and the associated ‘‘military revolution’’ that took place beginning in the late Middle Ages reduced the value of medieval fortifications. The main technological innovation was the introduction and improvement of gunpowder weapons, which began in the fourteenth century but only really began to have a serious impact in the fifteenth century with the introduction of iron cannonballs.

This is not a new insight, but it does align well with their model. However, it somewhat reverses the logic of the conventional view, which is that greater state power, along with military technology, reduced the prevalence of private castles. Instead, in Desierto and Koyama's model, the rise of gunpowder reduces the ability of lords to retreat to a well-defended castle in the event of a rebellion (because the castle could not be as well-defended against cannons). This reduced the lords' bargaining power, giving the monarch and the centralised state greater power. As a result, the state should become less stable. In support of this, Desierto and Koyama use the Wars of the Roses in England as an example:

England experienced a large number of rebellions and civil wars between 1450 and 1500. These conflicts are conventionally grouped under the label of the Wars of the Roses (1455–1485), but the period of weak state capacity and frequent rebellion extended from Jack Cade’s uprising in 1450 through Perkin Warbeck’s invasion and the Second Cornish Uprising in 1497. The causes of these rebellions were complex, multifaceted, and varied across cases. Nonetheless, the frequency of civil war during this period is consistent with our model’s prediction that a decline in the military value of castles would destabilize feudal realms.

And so, as gunpowder reduced the military value of castles, private castles became much less useful as a source of bargaining power for lords. That helps explain why the medieval pattern of widespread private castles gave way to state-controlled castles from the mid-15th Century onwards. Now, I'll be thinking more carefully about the vintage of the castles I visit on my next trip to Europe next month!